"Everybody was a little bit scared," said Luis Montalvo, a senior, talking about what was most definitely not just another day of class for the 1,300 students here at Northern Valley High's Demarest campus.

All day long, police kept a large blanket of security wrapped around this school after the anonymous tip that there would be a shooting sometime this week by as many as four boys.

"It was really secure," said JT Kim, a senior who added that he felt safe with the heavy police presence.

The tip led to a delayed start of school for these students as metal detectors were brought in overnight. During the day, they were under a sort of lockdown, no one allowed to leave for lunch, or even go outside for phys ed.

"Sadly because of what has happened in public schools around the country I don't take any of these things lightly," the school's Superintendent Dr. Jan Furman.

Many school districts, as we saw in Leonia last spring, have invited police in on off days to run their officers through active shooter exercises.

Here in Demarest, police have a sophisticated, nationally based tip line called 'We Tip' that has rarely been wrong...

"It was designed to weed out pranksters," said James Powderly, Demarest Police Chief

Since the threat was for anytime this week, more metal detectors were brought in, as well as two X-ray machines to speed the backpack check.

Oh, and the Police Chief says over the past five years, his department has a 100 per cent success rate in catching anyone who has posed a threat to this school.